1. Department of Physiology and Biophysics, State University of New York, Stony Brook, 11794-8661;
2. Department of Neuroscience, Albert Einstein College of Medicine, Bronx, New York 10461;
3. Department of Ophthalmology and Visual Sciences, University of Illinois at Chicago College of Medicine, Chicago, Illinois 60612;
4. Department of Chemical Sciences, University of Catania, 95125 Catania, Italy; and
5. Department of Neuroscience, Institut Pasteur, 75015 Paris, France